Fed Batch - Mass and Kinetic Balances

Question 1

What is the primary characteristic of a Fed Batch fermentation process?

Answer 1

There is flow in but no flow out. Thus volume changes.

Question 2

Why use a Fed Batch process?

Answer 2

1) To reduce the high-substrate inhibiting effect
2) To control the specific growth rate of a microorganism
3) To reach very high titers (compared to continuous especially)

Question 3

What are common products produced by a fed-batch process?

Answer 3

Bakers yeast, antibiotics, pharmaceutical proteins

Question 4

In order to keep the dilution rate constant, what do we do?

Answer 4

We change the feed flow rate exponentially so that D = F/V is constant.

Question 5

What happens is the feed flow rate is linear?

Answer 5

The specific growth rate decreases

Question 6

What is the equation for the feed flow rate with time?

Answer 6

F(tP) = [(Ysx u)/(csf - cs)]Vo xo e^(u t)

Question 7

What are the limitation to how long a fed-batch can run?

Answer 7

1) Air mass transfer (DO, OUR)
2) Cooling of the fermenter
3) Volume of the fermenter

Question 8

How can a fed-batch be operated “continuously”?

Answer 8

Through a repeated fed-batch process where some of the broth is drained off periodically.

Question 9

When is linear feed flow used?

Answer 9

When mass transfer and cooling are issues

Question 10

What other option can be used with the feed flow to address issues?

Answer 10

A “less steep” exponential feed is also possible, where the growth rate won’t be constant but also won’t decrease as much as with a linear flow.